1. Field of the Invention
The present invention relates to a vibration generator for a soil compacting device.
2. Description of the Related Art
For compacting soil, among others vibration plates known as “plate compactors” are known. In plate compactors, a vibration generator is seated in off-center fashion on a soil contact plate. The vibration generator is standardly a rotating imbalance shaft. The imbalance force, or centrifugal force, produced by the imbalance shaft pulls the soil contact plate (because of the off-center placement) upwards on one side and towards the front before the contact plate is pressed downward again, communicating the compacting energy to the soil. The vibration generator, which has a very simple construction, is thus able not only to produce the vibration required for the soil compacting, but also to move the soil contact plate forward.
Plate compactor plates of this type have outstanding movement behavior, in particular on difficult soil surfaces containing a high proportion of clay and high water content. Precisely on such cohesive soils, vibration plates having other designs can experience difficulty in moving forward. The advantageous characteristic of plate compactor plates is due to a comparatively large amplitude of the vibration generator, and to the presence of a constant reaction moment that, given a suitable direction of rotation of the imbalance shaft, permanently effects a determinate friction on the end of the soil contact plate situated opposite the vibration generator.
However, this design has turned out to have the disadvantage that it is not possible, using reasonably economical means, to execute a continuous reversing, i.e. a traveling back and forth, of the vibration plate, with the possibility of compacting at a point, i.e., purposive compacting at one location without forward movement of the vibration plate.
It is true that it is possible to situate imbalance shafts at the two opposite ends of the soil contact plate, and to drive only one of the two for forward or backward movement. However, in this case the imbalance shafts must be operated synchronously at double power consumption and with precise rotational speed, both for the stationary point compacting and for the transition from forward travel to backward travel, so that a considerable energy and control expense is required.